This invention relates generally to the collection and handling of dust and more particularly is concerned with the means and methods for collecting dust in the environment of a papermaking machine and for transporting the dust from the machine environment after the dust has been collected.
In a room in which a papermaking machine is used for making tissue, a relatively large amount of dust (including cellulose fiber, clay, starch and other chemical dust) may be released into the surrounding air by the papermaking process, and this released dust can create operating hazards, worker health hazards, and is likely to migrate to various areas of the room and create a cleanliness (e.g. machine hygiene) problem or increase the risk of fire at those areas. Heretofore, attempts to control the amount of dust released into a papermaking machine room involved the capturing of dust adjacent the source of creation (referred to herein as primary dust control) and the containing of dust after the dust has become airborne (referred to herein as secondary dust control). The systems and methods with which this invention is to be compared include the systems and methods employed for primary dust control and for secondary dust control.
Conventional primary and secondary dust control schemes commonly involve a fan or similar means for creating a vacuum at a collector, or vacuum head, through which dust and/or dust-laden air is drawn into the interior of the collector and subsequently transported from the collector by way of attending ductwork. To effectively carry the dust particles within the airstream, relatively high transport velocities are employed within the ductwork. In addition, wet-scrubbing equipment is commonly connected to the ductwork at a site downstream of the collector for wet-scrubbing the dust-laden air in a manner which separates dust from the air so that the air which is subsequently discharged to the atmosphere is relatively clean.
Limitations and disadvantages attending the conventional primary and secondary dust control schemes of the aforedescribed class relate to system operation, safety from fires, and cost. For example, the likelihood is high that the ductwork through which the dust and dust-laden air is transported will become fouled, or clogged, with dust so that design volumetric flow rates cannot be maintained. Furthermore, the cleanliness of the interior of the collectors and the attending ductwork can be adversely affected by moisture present within the dust-laden airstream. Low moisture levels will cause the dry dust particles to attach themselves to each other and/or the interior surface of the ductwork. Low moisture levels in the airstream are typically caused by intermittent introduction of water or high humidity levels at the inlet of the collector. Further still, water may be inadvertently and intermittently introduced into the inlets of the collectors during a cleanup operation performed around the machine. Consequently, the collectors and attending ductwork of these conventional dust control schemes require frequent and costly cleaning.
Furthermore, ductwork fouling, in conjunction with the high air flows, creates a situation in which a fire, if ignited (e.g. by mechanical friction or static charges) and not extinguished immediately, could propagate and damage components throughout the system, as well as present a high risk to human safety. Fire suppression equipment can be installed within the system to reduce the damage and safety risks of ductwork fires, but such equipment is relatively expensive, is rarely one-hundred percent effective, and must be routinely maintained in order to preserve the operating effectiveness that it possesses.
Further still, wet-scrubbing equipment which is commonly employed with conventional dust control systems is relatively expensive, and its cost, along with the cost of associated access platforms, support structures and installation, is likely to comprise a significant portion of the capital cost of the entire dust-collection system.
It is an object of the present invention to provide a new and improved means and method for collecting dust in the environment of a papermaking machine and which overcomes the disadvantages and limitations associated with conventional dust-collection schemes.
Another object of the present invention is to provide such a means and method which can be used for either primary or secondary dust control.
Still another object of the present invention is to provide such a means and method which reduces the likelihood of ductwork fouling, reduces the risk of a ductwork fire, and obviates the need for costly fire suppression equipment.
Yet another object of the present invention is to provide such a means and method which permits the relatively costly wet-scrubbing equipment to be replaced with a less costly droplet separator.
A further object of the present invention is to provide such a means which is uncomplicated in construction yet effective in operation.